Pyarthrosis of a child's hip can lead to osteonecrosis of the femoral head. Symptomatic treatment options for this condition are limited. We supposed that free vascularized fibula autografting would improve range of motion, decrease pain, and increase function in patients with symptomatic osteonecrosis of the pediatric femoral head secondary to pyarthrosis. We prospectively evaluated seven consecutive patients who presented with Stages IV and V osteonecrosis of the femoral head. All patients were treated with free vascularized fibular autografting to the femoral head. Postoperative evaluations of range of motion, pain symptoms, and functional activity showed improvements in all patients. Range of motion of the hip was significantly improved in the arcs of flexion (+23 degrees) and external rotation (+22 degrees). Harris hip scores significantly increased from an average preoperative score of 68 to an average postoperative score of 96. No patients needed revision surgery to hip arthrodesis or arthroplasty within the 3-year 11-month followup.